全文获取类型
收费全文 | 640篇 |
免费 | 31篇 |
国内免费 | 9篇 |
专业分类
化学 | 491篇 |
晶体学 | 3篇 |
力学 | 25篇 |
数学 | 34篇 |
物理学 | 127篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 27篇 |
2017年 | 18篇 |
2016年 | 35篇 |
2015年 | 21篇 |
2014年 | 35篇 |
2013年 | 100篇 |
2012年 | 42篇 |
2011年 | 45篇 |
2010年 | 46篇 |
2009年 | 36篇 |
2008年 | 34篇 |
2007年 | 27篇 |
2006年 | 32篇 |
2005年 | 14篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 21篇 |
2001年 | 6篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1975年 | 1篇 |
排序方式: 共有680条查询结果,搜索用时 31 毫秒
101.
Soghra Farzipour Mina Saeedi Mohammad Mahdavi Hossein Yavari Mohammadreza Mirzahekmati Nasser Ghaemi 《合成通讯》2014,44(4):481-487
Clean and easy preparation of quinazolin-4(3H)-one derivatives using 2-aminobenzamides and Vilsmeier reagent is described. 2-Aminobenzamides were converted into the corresponding quinazolinones under mild and efficient conditions, in good yields without undesirable by-products.
[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] 相似文献
102.
Molecular dynamics simulations were conducted to predict the structural properties and phase transition temperatures of n-alkanethiols CH(3)(CH(2))(n-1)SH (Cn, 4 ≤ n ≤ 22) self-assembled monolayers (SAMs) on Au (111) surfaces. We studied the effects of chain length on the structural properties, including tilt and orientation angles, and on phase transition temperature. We found clear dependence of the structural properties, on both the number of carbon atoms, n; and on n being odd or even. Alkanethiols with n ≤ 7 show liquid-like behavior and large rotational mobility, whereas those with n ≥ 12 are well-ordered and stable. For 12 ≤ n ≤ 15, odd-even effects are observed, where for n = odd, larger tilt angles, oriented in the direction of their next next nearest neighbor (NNNN), and for n = even, lower tilt angles, mostly tilted toward next nearest neighbor (NNN), were observed. For 15 ≤ n ≤ 19, we find tilt angle and orientation to be independent of n. For all alkanethiols, a gradual decrease of the tilt angle occurred by increasing the temperature from 300 to 420 K. Order-disorder phase transitions occurred at a certain temperature. This was signified by abrupt instabilities in the tilt orientation angle. This transition temperature showed an enhancement of ~67-100 °C over the melting point of the corresponding n-alkane bulk system. This enhancement depended on n, and was larger for n = odd. Overall, we found that odd alkanethiols show better structural and thermal stability, and smaller gauche defects. 相似文献
103.
Ramin Ghorbani-Vaghei Rahman Karimi-NamiZahra Toghraei-Semiromi Mostafa AmiriMehdi Ghavidel 《Tetrahedron》2011,67(10):1930-1937
N, N, N′, N′-Tetrabromobenzene-1,3-disulfonamide and poly(N-bromo-N-ethylbenzene-1,3-disulfonamide) were used as efficient catalysts for the one-pot synthesis of aliphatic and aromatic 2H-indazolo[2,1-b]phthalazine-triones in excellent yields from aldehydes, phthalhydrazide, and dimedone at 80-100 °C under solvent-free conditions. 相似文献
104.
S.A. Mirkhani M. Vossoughi G.R. Pazuki A.A. Safekordi A. Heydari J. Akbari M. Yavari 《The Journal of chemical thermodynamics》2011,43(10):1530-1534
(Liquid + liquid) equilibrium (LLE) data for the ternary systems (heptane + toluene + 1-ethyl-3-methylpyridinium ethylsulfate) and (heptane + benzene + 1-ethyl-3-methylpyridinium ethylsulfate) were measured at T = 298.15 K and atmospheric pressure. The selectivity and aromatic distribution coefficients, calculated from the equilibrium data, were used to determine if this ionic liquid can be used as a potential extracting solvent for the separation of aromatic compounds from heptane. The consistency of tie-line data was ascertained by applying the Othmer–Tobias and Hand equations. 相似文献
105.
An efficient protocol for the one‐pot reaction of isatoic anhydride (=1,2‐dihydro‐4H‐3,1‐benzoxazine‐2,4‐dione), primary alkylamines, and heterocumulenes (isothiocyanates and isocyanates) in H2O catalyzed by magnetically recoverable Fe3O4 nanoparticles is described. 相似文献
106.
Shirgholami MA Khalil-Abad MS Khajavi R Yazdanshenas ME 《Journal of colloid and interface science》2011,359(2):530-535
Superhydrophobic cotton textiles are prepared by a simple, one-step and inexpensive phase separation method under ambient conditions by which a layer of polymethylsilsesquioxane (PMSQ) nanostructures is covered onto the cellulose fibers. By changing the silane precursor concentration, PMSQ nanostructures with various shapes, morphologies and sizes were fabricated. Nanostructures were characterized using SEM, EDS, and attenuated total reflectance FTIR. The wettability of the modified cellulose surfaces was characterized with contact-angle goniometry and sliding angle technique, respectively. The water contact angle of modified cotton is measured to be higher than 150°, which is high enough to exhibit the lotus effect as a result of the superhydrophobicity. Tunable water-repellent properties of the fabric are also demonstrated, with sliding contact angles varying from "sticky" to "slippery" depending upon different nanostructures on the surface of the fibers. It is expected that this simple technique will accelerate the large-scale production of superhydrophobic cellulosic materials with new industrial applications. 相似文献
107.
Behzad Ramin Salehi Rad Mohammad Reza Nematollahi Nader 《Methodology and Computing in Applied Probability》2019,21(4):1045-1056
Methodology and Computing in Applied Probability - We consider a queueing system where some customers decide to simultaneously wait in two queues, rather than in a single queue, to receive their... 相似文献
108.
Issa Yavari Zinatossadat Hossaini Samereh Seyfi Faezeh Shirgahi-Talari 《Monatshefte für Chemie / Chemical Monthly》2008,139(10):1257-1259
The reaction of acetylenic esters with ethyl bromopyruvate in the presence of tetramethylthiourea led to highly functionalized
thiophenes in excellent yields.
Correspondence: Issa Yavari, Chemistry Department, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran. 相似文献
109.
110.